The conversion of the dominant recycle stream (about 60% of the weight) from crushing lead acid batteries to a useful product has been costly, highly energy intensive and generates considerable hazardous dust sulfur dioxide and carbon dioxide and carbon monoxide pollution when performed as it is in the smelters. The recovered lead metal from the grids is simply smelted while the lead sulfate/red lead/lead metal powder paste containing antimony and barium sulfate waste must be mixed with carbon and smelted in the furnaces along with the lead metal grid to achieve a practical and the lowest cost route currently for handling the paste material. That barium sulfate is usually added at 0.5 to 2% levels in lead acid batteries to control lead sulfate crystal size during electrode charging/discharging. The smelting with carbon converts the lead sulfate to sulfur dioxide which must be scrubbed and along with the extra lead dust and carbon powder which is generated. This is also a very energy intensive and polluting process. A better way is needed particularly when the smelters are under intense pressure to cut their emissions of particulate especially lead and sulfur dioxide.
The lead metal from the smelters is purified by sparging and forming a flux which carries out contaminates resulting in further losses and costs. For the electrodes in making lead acid batteries, a form of litharge is produced by the slow oxidation of molten lead metal (99.999% purity) at 400-500° C. to form an impure form of a mix of litharge and containing fine lead metal particles at 15-30% by weight. It is too expensive and too much time is required to try to oxidize this remaining lead to the litharge. The desired form of the PbO is the litharge (tetragonal-yellow-orange color) allotrope. This process also forms some of the white high temperature form called massicot, which is not desired, because of its slower reaction during electrode formation.
In U.S. Pat. No. 4,222,769 spent battery paste is desulfurized and then transformed into metallic lead by roasting in the presence of a carbon reducing agent.
U.S. Pat. No. 4,769,116 discloses treating exhausted lead acid battery paste with sodium hydroxide to produce a solution of sodium sulfate and a desulfurized paste which is subjected to electro winning to produce metallic lead.
U.S. Patent Publication No. 2006/0239903 to Guerriero discloses high purity lead hydroxide and lead oxide from spent acid battery paste that has been desulfurized and converted into a carbonate or hydroxide and then calcinated at 500° C. to obtain pure PbO. The multi-step process includes subsequent treating with acetic acid. The lead acetate solution was treated with an alkali or alkaline earth hydroxide to produce lead hydroxide.
U.S. Patent Publication No. 2010/043600 to Martini discloses a process for recovery of high purity lead compounds from electrode paste slime. The process includes dissolving lead oxide in the paste in suitable acid, reducing any insoluble lead dioxide with hydrogen peroxide, a sulfite or sulfurous anhydride, converting the lead oxide to lead sulfate and then treating the lead sulfate in a solution containing an acetate, calcinating the desulfurized material to get impure lead monoxide followed by leaching of the lead monoxide with acetic acid followed by filtering and then treating further with an alkali hydroxide or alkaline earth hydroxide to obtain soluble acetates to get a precipitate of lead hydrate or lead monoxide.
U.S. Pat. No. 7,507,496 to Smith et al relates to the selective removal of sulfate from battery paste and recovering Pb3O4 which has small amounts of impurities and can be separated from the impurities by dissolution.
U.S. Pat. No. 5,211,818 discloses a process wherein the paste sludge resulting from the exhausted batteries is treated with a solution of ammonium sulfate and the metallic lead constituent is recovered by electrowinning.
International Publication No. WO99/44942 discloses a process of producing lead monoxide from spent lead batteries using fluxing agents and an organic reducer in the calcinations step at a temperature of 400° C.-450° C.
Typically litharge is made in the Barton process by heating lead metal to 380-500° C. to keep it molten and passing controlled amounts of air or oxygen through it to partially oxidize it to litharge containing 25% lead with strong agitation. The lead oxide (litharge) that forms initially contains very fine lead metal which is intimately mixed into the litharge/massicot lead oxide mix which more slowly reacts in positive electrode plate formation.